Method and apparatus for transmitting and receiving a signal in a wireless communication system

ABSTRACT

A method includes receiving, by a user equipment (UE) and through Radio Resource Control (RRC) signaling, information of a resource pool for a D2D communication, wherein the information of the resource pool comprises information of a discovery subframe in which a D2D discovery signal is to be communicated, determining that in the discovery subframe, the D2D discovery signal is prioritized over a communication with an evolved NodeB (eNB) unless the communication with the eNB is associated with a random access (RA) procedure, transmitting a RA preamble through a Physical Random Access Channel (PRACH), determining whether the discovery subframe corresponds to a RA subframe in which a RA response for the UE is to be monitored, and in response to determining that the discovery subframe corresponds to the RA subframe, monitoring, by the UE, the RA response during the discovery subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/427,388, filed on Feb. 8, 2017, which is a continuation ofInternational Patent Application No. PCT/KR2015/008256, filed on Aug. 6,2015, which claims priority from and the benefit of Korean PatentApplication No. 10-2014-0102674, filed on Aug. 8, 2014, each of which ishereby incorporated by reference in its entirety.

BACKGROUND 1. Field

The present disclosure relates to wireless communication, and moreparticularly, to a method and apparatus for selectively transmitting andreceiving a user equipment (UE)-to-UE signal and a UE-to-evolved node B(eNB) signal in a wireless communication system.

2. Discussion of the Background

Long term evolution (LTE) of the 3^(rd) generation partnership project(3GPP) allows supporting a proximity service (ProSe) in order to satisfythe needs of public safety agencies. The LTE system requires technologythat provides backward and/or forward compatibility because discoverytechnology and broadcasting communication have been added to aproximity-based service. A representative technology of aproximity-based application technology is device to device (D2D)communication, which has been utilized since the emergence of the analogradio set.

However, the D2D communication in a mobile wireless communicationsystem, e.g., LTE, LTE-A, is distinct from existing D2D communicationsystems. The D2D communication in a mobile wireless communication systemindicates communication that directly transmits and receives databetween UEs without passing through an infrastructure node (e.g., aneNB) of the wireless communication system. That is, each of two UEsbecomes a source and a destination of direct data communicationtherebetween. D2D communication may efficiently use a limited amount ofradio resources, may reduce the load of the wireless communicationsystem, and may enable communication without a network, which is anadvantage.

D2D communication may be performed using a communication scheme thatuses a non-licensed band such as Bluetooth or a wireless LAN. However,communication schemes that use non-licensed bands have difficultyproviding a planned and controlled service, which is a drawback.Particularly, performance may be dramatically reduced by interference.Conversely, device-to-device direct communication, which may be operatedor provided in a licensed band or an environment where inter-systeminterference is under control, may be capable of ensuring quality ofservice (QoS), raising frequency utilization efficiency throughfrequency reuse, and increasing a distance in which the communicationbetween the devices is reliable.

In the D2D communication of the wireless communication system describedabove, a UE having a single transceiver chain is incapable of performingtransmission or reception in multiple bands in parallel. Therefore,there is a need for a method of efficiently transmitting and receiving aD2D signal while reducing any burden or restrictions on an existing LTEsignal in the LTE frequency band (FDD/TDD).

SUMMARY

An aspect of the present disclosure is to provide a method and apparatusfor multiplexing a signal in a wireless communication system thatsupports D2D communication.

Another aspect of the present disclosure is to provide a method andapparatus for selectively transmitting or receiving a user equipment(UE)-to-UE signal and a UE-to-evolved node B (eNB) signal in a wirelesscommunication system that supports D2D communication.

Another aspect of the present disclosure is to provide a method andapparatus for selectively transmitting or receiving a D2D receptionsignal and a WAN reception signal in a wireless communication systemthat supports D2D communication.

Another aspect of the present disclosure is to provide a method andapparatus for selectively transmitting or receiving a D2D receptionsignal and a WAN transmission signal in a wireless communication systemthat supports D2D communication.

Another aspect of the present disclosure is to provide a method andapparatus for selectively transmitting or receiving a D2D transmissionsignal and a WAN transmission signal in a wireless communication systemthat supports D2D communication.

Another aspect of the present disclosure is to provide a method andapparatus for selectively transmitting or receiving a D2D transmissionsignal and a WAN reception signal in a wireless communication systemthat supports D2D communication.

An exemplary embodiment provides a method of performing a random accessprocedure during a device-to-device (D2D) discovery period, the methodincluding: receiving, by a user equipment (UE) and through RadioResource Control (RRC) signaling, information of a resource pool for aD2D communication, wherein the information of the resource pool includesinformation of a discovery subframe in which a D2D discovery signal isto be communicated; determining that in the discovery subframe, the D2Ddiscovery signal is prioritized over a communication with an evolvedNodeB (eNB) unless the communication with the eNB is associated with arandom access (RA) procedure; transmitting a RA preamble through aPhysical Random Access Channel (PRACH); determining whether thediscovery subframe corresponds to a RA subframe in which a RA responsefor the UE is to be monitored; and in response to determining that thediscovery subframe corresponds to the RA subframe, monitoring, by theUE, the RA response during the discovery subframe.

An exemplary embodiment provides a method of performing a random accessprocedure during a device-to-device (D2D) discovery period, the methodincluding: determining, by a user equipment (UE), a discovery periodincluding one or more of a discovery transmission subframe or adiscovery reception subframe, wherein the discovery transmissionsubframe is configured for the UE to transmit a D2D discovery signal todiscover a different UE, and the discovery reception subframe isconfigured for the UE to monitor reception of a D2D discovery signaltransmitted from a different UE; determining that in the discoveryperiod, a D2D discovery communication between UEs is prioritized over aWide Area Network (WAN) communication with an evolved NodeB (eNB) unlessthe WAN communication with the eNB is associated with a random access(RA) procedure; transmitting a RA preamble through a Physical RandomAccess Channel (PRACH); determining a RA response monitoring period inwhich a RA response for the UE is to be monitored; and in response todetermining that at least part of the RA response monitoring periodoverlaps the discovery period, monitoring, by the UE, the RA responseduring the overlapped discovery period.

An exemplary embodiment provides a method of performing a random accessprocedure during a device-to-device (D2D) discovery period, the methodincluding: receiving, by a user equipment (UE) and through RadioResource Control (RRC) signaling, information of a resource pool for aD2D communication, wherein the information of the resource pool includesinformation of a discovery subframe in which a D2D discovery signal isto be communicated; determining that in the discovery subframe, the D2Ddiscovery signal is prioritized over a communication with an evolvedNodeB (eNB) unless the communication with the eNB is associated with arandom access (RA) procedure; transmitting a RA preamble through aPhysical Random Access Channel (PRACH); determining a RA responsereceived during a RA monitoring period in which the RA response for theUE is to be monitored; determining whether the discovery subframecorresponds to a RA subframe in which a message responsive to the RAresponse for the UE is to be processed; and in response to determiningthat the discovery subframe corresponds to the RA subframe, processing,by the UE, the message responsive to the RA response during thediscovery subframe.

According to the present disclosure, although a user equipment (UE) haslimited capacity (e.g., a single transceiver chain), the UE may becapable of multiplexing D2D ProSe Direct Communication and D2D discoveryin a band/cell that supports legacy LTE signals.

According to the present disclosure, a system may be capable ofreceiving a larger number of D2D UEs without a significant decrease inthe quality of a legacy LTE signal, irrespective of the RF capacity of acell managed by a corresponding network. Therefore, a D2D UE may bedeployed more quickly and the legacy LTE market volume may increase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the present disclosure.

FIGS. 2 and 3 are diagrams schematically illustrating the structure of aradio frame according to the present disclosure.

FIG. 4 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

FIG. 5 is a diagram illustrating an example of a D2D discovery resourceaccording to the present disclosure.

FIG. 6 is a diagram illustrating examples of a D2D discovery resourceset according to the present disclosure.

FIG. 7 is a diagram illustrating examples of a structure of a D2Ddiscovery resource configuration in a D2D discovery resource setaccording to the present disclosure.

FIGS. 8 to 12 are diagrams illustrating an information delivery betweenUEs and eNBs for D2D communication according to the present disclosure.

FIGS. 13 to 16 are diagrams illustrating embodiments of multiplexing aWAN Rx and a D2D Rx associated with a D2D discovery signal.

FIGS. 17 and 18 are diagrams illustrating examples of applyingmultiplexing of a D2D Rx and a WAN Rx to a plurality of discoveryresources according to the present disclosure.

FIG. 19 is a diagram illustrating an example (2-1) of multiplexing a D2DRx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

FIG. 20 is a diagram illustrating another example (2-2) of multiplexinga D2D Rx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

FIG. 21 is a diagram illustrating another example (2-3) of multiplexinga D2D Rx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

FIG. 22 is a flowchart illustrating operations of a UE according to thepresent disclosure.

FIG. 23 is an apparatus block diagram illustrating a wirelesscommunication system according to the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the present disclosure.

Referring to FIG. 1, a wireless communication system 10 is widelyinstalled to provide various communication services such as a voiceservice, a packet data service, or the like. The wireless communicationsystem 10 includes at least one evolved node B 11 (eNB). Each eNB 11provides a communication service with respect to a predetermined cell 15a, 15 b, and 15 c. A cell may be divided into a plurality of areas(referred to as sectors).

A user equipment (UE) 12 may be fixed or may have mobility, and may bereferred to by another term, such as a mobile station (MS), a mobileterminal (MT), a user terminal (UT), a subscriber station (SS), awireless device, a personal digital assistant (PDA), a wireless modem, ahandheld device, or the like. The eNB 11 may be referred to by anotherterm, such as a base station (BS), a base transceiver system (BTS), anaccess point, a femto base station, a home node B, a relay, or the like.A cell is a concept including various types of coverage areas, such as amegacell, a macrocell, a microcell, a picocell, a femtocell, and thelike.

Hereinafter, a downlink (DL) indicates communication from the eNB 11 tothe UE 12, and an uplink (UL) indicates communication from the UE 12 tothe eNB 11. In a downlink, a transmitter may be a part of the eNB 11 anda receiver may be a part of the UE 12. In an uplink, a transmitter maybe a part of the UE 12 and a receiver may be a part of the eNB 11. Amultiple access scheme applied to a wireless communication system maynot be limited. Various multiple access schemes, such as Code DivisionMultiple Access (CDMA), Time Division Multiple Access (TDMA), FrequencyDivision Multiple Access (FDMA), Orthogonal Frequency Division MultipleAccess (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, orOFDM-CDMA, may be used. An uplink transmission and a downlinktransmission may use a Time Division Duplex (TDD) scheme that performstransmissions at different times, or may use a Frequency Division Duplex(FDD) scheme that performs transmissions at different frequencies.

The layers of a radio interface protocol between a UE and an eNB may bedistinguished as a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the well-known open systeminterconnection (OSI) model in a communication system. Among them, aphysical layer belonging to the first layer may provide an informationtransfer service using a physical channel.

The physical layer may be connected to a higher Media Access Control(MAC) layer through a transport channel. Data may be transferred throughthe transport channel between the MAC layer and the physical layer. Thetransport channel may be classified based on how data is transferredthrough a wireless interface. Also, data may be transferred through aphysical channel between different physical layers (that is, thephysical layers of a UE and an eNB). The physical channel may bemodulated based on an Orthogonal Frequency Division Multiplexing (OFMD)scheme, and may utilize a space formed based on time, frequencies, and aplurality of antennas as a radio resource.

FIGS. 2 and 3 are diagrams schematically illustrating the structure of aradio frame according to the present disclosure. Particularly, FIG. 2 isa diagram illustrating the concept of cellular network-based D2Dcommunication system according to the present disclosure, and FIG. 3 isa diagram illustrating an example of the structure of a D2D discoveryresource configuration. Referring to FIGS. 2 and 3, a single radio frameincludes 10 subframes, and a single subframe includes two consecutiveslots. A basic time (length) unit for controlling transmission in aradio frame is referred to as a transmission time interval (TTI). TTImay be 1 ms. The length of a single subframe (1 subframe) may be lms,and the length of a single slot (1 slot) may be 0.5 ms.

A single slot may include a plurality of symbols in the time domain. Forexample, in a wireless system that uses Orthogonal Frequency DivisionMultiple Access (OFDMA) in the downlink (DL), the symbol may be anOrthogonal Frequency Division Multiplexing (OFDM) symbol. In a wirelesssystem that uses Single Carrier-Frequency Division Multiple Access(SC-FDMA) in the uplink (UL), the symbol may be an SC-FDMA symbol. Anexpression associated with a symbol period of the time domain may not belimited by a multiple access scheme or name.

The number of symbols included in a single slot may be different basedon the length of a cyclic prefix (CP). For example, in the case of anormal CP, seven symbols are included in a single slot. In the case ofan extended CP, six symbols are included in a single slot.

A resource element (RE) refers to the minimum time-frequency unit towhich a modulated symbol of a data channel, a modulated symbol of acontrol channel, or the like is mapped. A resource block (RB) is aresource allocation unit, and may include a time-frequency resourcecorresponding to 180 kHz in the frequency axis and a single slot in thetime axis. The RB may be referred to as a physical resource block (PRB).A resource block pair indicates a resource block unit that includes twoconsecutive slots in the time axis.

Various physical channels may be used in the physical layer; thephysical channels may be mapped to the radio frame and transmitted. As adownlink physical channel, a Physical Downlink Control Channel(PDCCH)/Enhanced PDCCH (EPDCCH) may inform a UE of resource allocationof a Downlink Shared Channel (DL-SCH) and a Paging Channel (PCH), aswell as Hybrid Automatic Repeat Request (HARQ) information associatedwith the DL-SCH. The PDCCH/EPDCCH may carry an uplink grant that informsa UE of the resource allocation of an uplink transmission. The PDCCH andthe EPDCCH are mapped to different resource areas. A DL-SCH may bemapped to a Physical Downlink Shared Channel (PDSCH) A Physical ControlFormat Indicator Channel (PCFICH) informs a UE of the number of OFDMsymbols used for a PDCCH, and is transmitted for each subframe. APhysical Hybrid ARQ Indicator Channel (PHICH) is a downlink channel, andcarries a Hybrid Automatic Repeat ReQuest (HARQ) Acknowledgement(ACK)/Non-acknowledgement (NACK) signal, which is a response to anuplink transmission. A HARQ ACK/NACK signal may be referred to as aHARQ-ACK signal.

As an uplink physical channel, a Physical Random Access Channel (PRACH)carries a random access preamble. A Physical Uplink Control Channel(PUCCH) carries uplink control information, such as channel statusinformation (CSI) indicating a downlink channel status, for example, achannel quality indicator (CQI), a precoding matrix index (PMI), aprecoding type indicator (PTI), a rank indicator (RI), and a HARQ-ACKwhich is a response to a downlink transmission. A Physical Uplink SharedChannel (PUSCH) carries an Uplink Shared Channel (UL-SCH).

Uplink data may be transmitted on the PUSCH; this uplink data may be atransport block (TB) that is a data block for a UL-SCH transmittedduring a transmission time interval (TTI). The TB may include user data.Alternatively, uplink data may be multiplexed data. Multiplexed data maybe obtained by multiplexing a transport block for a UL-SCH and uplinkcontrol information; that is, when user data that needs to betransmitted in the uplink exists, uplink control information may bemultiplexed with the user data and may be transmitted through the PUSCH.

Recently, a method for supporting D2D communication has been consideredwherein UEs utilize transmission/reception technologies of a wirelesscommunication system in the frequency band of the wireless communicationsystem or other bands, and directly exchange user data between the UEswithout passing through an infrastructure node (for example, an eNB).This D2D communication may allow for wireless communication in an areaoutside the limited wireless communication infrastructure, and mayreduce loads on the wireless communication network. Also, the D2Dcommunication may provide disaster information to UEs even when eNBs donot smoothly operate under war or disaster situations, which is anadvantage.

A UE that transmits a signal based on the D2D communication is definedas a transmission UE (Tx UE), and a UE that receives a signal based onthe D2D communication is defined as a reception UE (Rx UE). The Tx UEtransmits a discovery signal, a D2D control signal, or a D2D datasignal. The Rx UE receives a discovery signal, a D2D control signal, ora D2D data signal. The Tx UE and the Rx UE may operate by exchangingtheir roles. A signal transmitted by the Tx UE may be received by two ormore Rx UEs. Alternatively, signals transmitted by two or more Tx UEsmay be selectively received by a single Rx UE. A D2D signal may betransmitted through an uplink resource. Therefore, a D2D signal may bemapped to an uplink subframe and may be transmitted from the Tx UE tothe Rx UE. The Rx UE may receive a D2D signal on the uplink subframe.

FIG. 4 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

Referring to FIG. 4, a cellular communication network including a firsteNB 410, a second eNB 420, and a first cluster 430 is configured. Afirst UE 411 and a second UE 412 included in a cell provided by thefirst eNB 410 may execute communication with a general access link(cellular link) through the first eNB 410. This is anin-coverage-single-cell D2D communication scenario. The first UE 411belonging to the first eNB 410 may execute D2D communication with afourth UE 421 belonging to the second eNB 420. This is anin-coverage-multi-cell D2D communication scenario. Also, a fifth UE 431belonging to the outside of a network coverage may generate singlecluster 430 with a sixth UE 432 and a seventh UE 433, and may performD2D communication with them. This is an out-of-coverage D2Dcommunication scenario. Here, the fifth UE 431 may operate as a clusterhead (CH) of the first cluster. A cluster head is a UE (or unit) used asa reference for at least the purpose of synchronization and,occasionally, indicates a UE that allocates a resource for differentpurposes. The cluster head may include an Independent SynchronizationSource (ISS) for the synchronization of out-of-coverage UEs.

Also, the third UE 413 may perform D2D communication with the sixth UE432, which corresponds to a partial-coverage D2D communication scenario.

D2D communication may include direct communication in which D2D UEstransmit and receive data and control information for the purpose ofpublic safety. To support the D2D communication, a D2D discoveryprocedure and a D2D synchronization procedure may be executed. A D2Ddiscovery signal may be used solely for commercial purposes (e.g.,advertising or the like).

To perform a D2D data transmission/reception through D2D communication,D2D control information needs to be transmitted/received between UEs.The D2D control information may be referred to as a schedulingassignment (SA) or D2D SA. A D2D Rx UE may perform a D2D data receptionbased on the SA. The SA may include, for example, at least one of: a newdata indicator (NDI), a target identification (target ID), a redundancyversion (RV) indicator, a modulation and coding scheme (MCS) indication,a resource pattern for transmission (RPT) indication, and a powercontrol indication.

Here, the NDI indicates whether a current transmission is a repetition(i.e., a retransmission) or a new transmission. A receiver may combinethe same data based on the NDI. The target ID indicates an ID ofterminals (UEs) to which a corresponding data MAC PDU is to betransmitted. The data MAC PDU may be transmitted through group castingor broadcasting based on the ID value, and may be transmitted eventhrough uni-casting based on the settings. The RV indicator indicates aredundancy version by specifying different start points in a circularbuffer for reading an encoded buffer. Based on the RV indicator, a Tx UEmay choose various redundancy versions associated with a repeatedtransmission of the same packet. The MCS indication indicates an MCSlevel for D2D communication. However, an MCS for D2D communication(e.g., SA or data) may be fixed to a QPSK. The RPT indication indicatesa time/frequency physical resource in which corresponding D2D data isallocated and transmitted. The power control indication is aninstruction used when a UE that receives corresponding informationcontrols the magnitude of power to be appropriate for a correspondingD2D transmission.

From the perspective of a Tx UE, the Tx UE may perform resourceallocation for D2D communication in two modes.

Mode 1 is the case in which an eNB or a relay node (hereinafter an eNBincludes a relay node) schedules predetermined resources for D2Dcommunication. That is, in mode 1, a predetermined resource used fortransmitting D2D data and D2D control information of a Tx UE may bedesignated by an eNB or a relay node. Mode 2 is the case in which a UEdirectly selects one or more predetermined resources from a resourcepool. That is, in mode 2, a Tx UE directly selects predeterminedresources to be used for transmitting D2D data and D2D controlinformation.

A D2D communication-enabled UE supports at least mode 1 or mode 2 forthe in-coverage D2D communication. The D2D communication-enabled UE maysupport mode 2 for the out-of-coverage or edge-of-coverage D2Dcommunication.

In mode 1, the location of a resource(s) for a D2D control informationtransmission and the location of a resource(s) for a D2D datatransmission are given by an eNB. That is, the same grant for a D2D SAtransmission and a data transmission is given from the eNB to a UEthrough the transmission of an (E)PDCCH in the form of a DCI messagehaving the same size as DCI format 0.

In mode 2, a resource pool for a D2D control information transmission(e.g., SA) may be pre-configured and/or semi-statically allocated. Inthis instance, a Tx UE may select a resource for D2D control informationfrom the resource pool so as to transmit the D2D control information.

D2D discovery may be performed on a D2D discovery resource. For example,a D2D UE may transmit a discovery signal through a discovery resource(hereinafter, D2D discovery resource) that is randomly selected (outsideof network coverage) or set by an eNB (inside of network coverage),within each discovery period. When a resource is randomly selected, aresource for transmitting a discovery signal may be determined based ona pre-configured or configured nominal transmission probability or basedon a fixed or adaptive transmission probability.

FIG. 5 is a diagram illustrating an example of a D2D discovery resourceaccording to the present disclosure.

Referring to FIG. 5, a single D2D discovery resource may be formed of ncontiguous PRBs and a single subframe in the frequency domain. n may be,for example, 2 or 3. In this instance, inter-slot frequency hopping isnot executed in the subframe.

A set of D2D resources may be used for a repeated transmission of aMedium Access Control Protocol Data Unit (MAC PDU) that delivers adiscovery signal (hereinafter referred to as a discovery MAC PDU) withina discovery period.

FIG. 6 is a diagram illustrating examples of a D2D discovery resourceset according to the present disclosure.

Referring to FIG. 6, a D2D discovery resource set within a discoveryperiod may include contiguous D2D discovery resources or non-contiguousD2D discovery resources, in the time domain. That is, repeated D2Ddiscovery resources in the D2D discovery resource set may be contiguousor non-contiguous in the time domain.

FIG. 7 is a diagram illustrating examples of a D2D discovery resourceconfiguration structure in a D2D discovery resource set according to thepresent disclosure.

Referring to FIG. 7, patterns indicate resources included in each D2Ddiscovery resource set. A plurality of D2D discovery resource sets mayexist in a single discovery period, and D2D discovery resources in asingle D2D discovery resource set may be contiguous or non-contiguous inthe time axis, and may be arranged in the frequency axis based onfrequency hopping (inter-subframe frequency hopping). From theperspective of an Rx UE, a discovery signal may be monitored within aresource pool for a D2D reception. The resource pool for a correspondingD2D reception may be in the form of a super set, when compared to aresource pool for a D2D transmission.

The definition of a discovery period may be distinguished based on adiscovery type, that is, discovery type 1 and discovery type 2B. In thecase of type 1, the discovery period indicates periodicity of resourcesallocated for a D2D discovery signal transmission within a cell. In thecase of type 2B, the discovery period indicates the periodicity ofresources for a D2D discovery signal reception from a cell. Multiplediscovery periods having various lengths may be used. In the case oftype 2B, a network may configure predetermined resources for D2Ddiscovery signal transmission.

To determine whether to transmit a D2D discovery signal, a D2D discoverytransmission probability may be set.

A D2D UE that executes a D2D discovery signal transmission may randomlyselect resources and transmit a discovery MAC PDU within a discoveryperiod. In this instance, the UE may not transmit a discovery MAC PDU inevery discovery period, but may determine whether to transmit adiscovery MAC PDU on a corresponding resource. The UE may determinewhether to transmit a MAC PDU on a corresponding resource based on a D2Ddiscovery transmission probability. The UE selects discovery resourcesin a discovery resource set within a set discovery period, randomly(type 1) or based on a network configuration (type 2), and repeatedlytransmits a discovery MAC PDU on the selected discovery resources.

For example, the D2D discovery transmission probability may bedetermined based on a period/offset. That is, a discovery period numberand a time/frequency offset are given, and the UE may transmit a D2Ddiscovery signal at a corresponding point.

As another example, the D2D discovery transmission probability may bebased on a fixed probability or an adaptive probability. (1) When it isbased on a fixed probability, whether to transmit a D2D discovery signalon a discovery resource may be determined based on a random functionincluding a probability value P. (2) When it is based on an adaptiveprobability, this case may be similar to the case based on the fixedprobability but the probability value P may adaptively vary. Forexample, when a D2D discovery signal transmission is not executed in aprevious period, the probability value P may increase by k, and when aD2D discovery signal transmission is executed, the probability value Pmay increase by m. Alternatively, the probability value P may increasegradually, and may decrease by a predetermined value when apredetermined condition is satisfied.

In the present disclosure, it is assumed that a D2D synchronizationSignal (D2DSS) and a Physical D2D Synchronization Channel (PD2DCH) arelocated in a resource that is configured by a network or determined inadvance in order to effectively support D2D discovery or D2Dcommunication. Therefore, when a D2DSS or a PD2DSCH is located in aresource for D2D discovery or D2D communication (SA/data), a D2D signaland a Wide Area Network (WAN) signal may be multiplexed in thecorresponding resource. The WAN refers to a network that configures awide coverage in an existing cellular network and provides mobile UEswith voice/data traffic. The WAN may correspond to WCDMA, LTE, WiMAX,and the like. Radio access networks are generally referred to as a WAN.

FIGS. 8 to 12 are diagrams illustrating delivery of information amongUEs and an eNB for D2D communication according to the presentdisclosure. As an example, FIGS. 8 to 12 are flowcharts showing resourceconfiguration and transmission/reception of signals among an eNB, a D2DTx UE, and a D2D Rx UE, in association with D2D discovery signals anddata communication.

FIG. 8 is a diagram illustrating a process in which an idle mode UEexecutes a type 1 D2D discovery transmission/reception in a wirelesscommunication system according to the present disclosure.

Referring to FIG. 8, a Tx UE and an Rx UE obtain information associatedwith a TX/RX resource pool from an eNB through an SIB in operations 810and 812. When the Tx UE and the Rx UE are in an idle mode, the eNBbroadcasts SIB information so as to provide the information associatedwith a resource pool for D2D communication.

The Tx UE determines to execute a discovery transmission in operation820, and selects a discovery resource of a predetermined time/frequencydomain for the discovery transmission, based on the obtained informationassociated with the resource pool, in operation 830. The discoveryresource may be selected based on a random function, and this may beidentified based on identification information of the UE. The Tx UEtransmits a discovery signal through the selected discovery resource inoperation 840. The Rx UE receives the discovery signal in operation 850.This may be referred to as discovery type 1.

FIG. 9 is a diagram illustrating a process in which an RRC-connectedmode UE executes a type 1 D2D discovery transmission/reception in awireless communication system according to the present disclosure.

When the UE has an RRC connection, type 1 discovery may be set through adedicated RRC signal, and an eNB may indicate corresponding resourcepool information.

Referring to FIG. 9, RRC-connected mode Tx UE and Rx UE request type 1discovery transmission grant from the eNB in operations 900 and 902. TheeNB determines a discovery grant request received from each UE, andgrants the request based on the context of a corresponding UE inoperation 905 and 907.

In this instance, the eNB transmits configuration information associatedwith type 1 (i.e., information associated with a Tx/Rx resource pool andthe like) through a dedicated signal to each of the RRC-connected modeTx UE and Rx UE, in operations 910 and 912. The Tx UE and the Rx UE arein an RRC-connected mode, and the eNB may transmit, to each UE, an RRCsignal in which configuration information for D2D discovery is includedin RRC configuration information.

Subsequently, the Tx UE determines to execute a discovery transmissionin operation 920, and selects a discovery resource of a predeterminedtime/frequency domain for the discovery transmission based on theobtained information associated with the resource pool in operation 930.The discovery resource may be selected based on a random function, andthis may be identified based on identification information of the UE.The Tx UE transmits a discovery signal through the selected discoveryresource in operation 940. The Rx UE receives the discovery signal inoperation 950. Here, FIG. 9 illustrates a process in which discoverytype 1 is executed.

FIG. 10 is a diagram illustrating an example of transmitting orreceiving type 2B D2D discovery signals in an RRC-connected mode in awireless communication system according to the present disclosure.

Referring to FIG. 10, D2D discovery type 2B is executed in anRRC-connected mode. The D2D discovery type 2B is executed in only anRRC-connected mode.

As an example, an eNB transmits information associated with type 2 andinformation associated with a Tx/Rx resource pool for type 2, through adedicated signal, to each of the RRC-connected mode Tx UE and Rx UE inoperations 1010 and 1012. As a matter of course, the eNB may allow forthe execution of type 2B discovery based on whether a corresponding UEis capable of executing type 2B discovery, or by request from a UE.

Accordingly, the Tx UE determines to execute a discovery transmission inoperation 1020, and selects/determines a discovery resource of apredetermined time/frequency domain, which is configured through thededicated signal in operation 1030.

Therefore, the Tx UE transmits a discovery signal through only theconfigured discovery resource in operation 1040. The Rx UE receives thediscovery signal in operation 1050. Here, FIG. 10 illustrates a processin which type 2 discovery is executed.

FIG. 11 is a diagram illustrating another process in which D2D datacommunication is executed in an RRC-connected mode in a wirelesscommunication system according to the present disclosure.

FIG. 11 illustrates a process of executing mode 2 ProSe directcommunication before executing mode 2 communication in an RRC-connectedmode. As an example, the mode 2 operation may be used for an exceptionalcase such as RLF, and mode 1 operation may be executed by default. Anidle mode UE executes the mode 2 operation based on informationindicated by the SIB.

Particularly, the RRC-connected mode Tx UE and the Rx UE request a ProSedirect communication transmission grant from an eNB in operations 1100and 1102. The eNB determines the ProSe direct communication transmissiongrant received from each UE, and grants the request based on the contextof a corresponding UE in operations 1105 and 1107.

The eNB transmits configuration information associated with mode 2 andinformation associated with a Tx/Rx resource pool for mode 2, through adedicated signal, to each of the RRC-connected mode Tx UE and Rx UE inoperations 1110 and 1112. When the Tx UE and the Rx UE are in anRRC-connected mode, the eNB may transmit to each UE an RRC signal thatincludes information for the mode 2 D2D data communication in the RRCconfiguration information.

The Tx UE determines to execute a communication transmission inoperation 1120, and selects/determines a resource for communication(SA/data), based on the obtained/configured resource pool information inoperation 1130.

Subsequently, the Tx UE transmits communication SA/data through theselected resource, in operation 1140. The Rx UE receives thecommunication data in operation 1150.

FIG. 12 is a diagram illustrating another process in which D2D discoveryis transmitted/received in an RRC-connected mode in a wirelesscommunication system according to the present disclosure.

FIG. 12 illustrates a process of executing mode 1 ProSe directcommunication before executing mode 1 communication in an RRC-connectedmode.

Particularly, the RRC-connected mode Tx UE and Rx UE request a ProSedirect communication transmission grant from an eNB in operations 1200and 1202 The eNB determines the ProSe direct communication transmissiongrant received from each UE, and grants the request based on context ofa corresponding UE in operations 1205 and 1207.

The eNB transmits configuration information associated with mode 1 andinformation associated with a Tx/Rx resource pool for mode 1, through adedicated signal, to each of the RRC-connected mode Tx UE and Rx UE inoperations 1210 and 1212. When the Tx UE and the Rx UE are in anRRC-connected mode, the eNB may transmit, to each UE, an RRC signal thatincludes information for the mode 1 D2D data communication in the RRCconfiguration information.

The Tx UE determines to execute a communication transmission inoperation 1220, and reports a buffer state associated with the D2D datathrough a ProSe BSR in operation 1224. The eNB that receives the ProSeBSR from the Tx UE may allocate a ProSe SA/ProSe data grant for a D2Ddata transmission. The ProSe SA/ProSe data grant may be indicatedthrough a PDCCH or an EPDCCH in operation 1228.

The Tx UE that obtains the ProSe SA/ProSe data grant selects/determinesa resource for communication (SA/data) based on information associatedwith the configured resource pool information and the SA/data grant inoperation 1230.

The Tx UE transmits ProSe SA/ProSe data (communication data) through theselected resource in operation 1240. The Rx UE receives thecommunication SA/data in operation 1250.

When a WAN signal transmission coexists while a service for D2D issupported, there is a need for a more effective data transmission andsignal transmission/reception scheme. To this end, multiplexing of a D2Dsignal and a WAN signal according to the present disclosure will bedescribed. For example, a method in which a UE having a singletransceiver chain multiplexes a D2D signal and a WAN signal in an LTEFDD band will be described. Hereinafter, the methods discussed in thepresent disclosure may be applied to a multi-carrier scenario.

For example, the present disclosure may be applied to multiplexing of aUE that has a single transceiver chain on a cellular spectrum (carrier#0) and an uplink spectrum (on FDD) for D2D. A D2D Tx/RX signal and aWAN Tx/Rx signal may be simultaneously transferred in the FDD band. Inassociation with multiplexing, the following four combinations arepossible: 1) D2D Rx & WAN Rx, 2) D2D Rx & WAN Tx, 3) D2D Tx & WAN Tx, 4)D2D Tx & WAN Rx. Hereinafter, the four combinations will be described asCase 1 through Case 4.

Case 1: Multiplexing D2D Rx and WAN Rx

A case of multiplexing a D2D RX on an uplink spectrum (D2D Rx on ULspectrum) and a WAN Rx on a downlink spectrum (WAN Rx on DL spectrum) inan FDD band will be described. The following descriptions may be appliedto a TDD band in a similar manner by using a subframe instead of aspectrum.

When a D2D UE is embodied to have an independent RF chain for a D2Dsignal and a WAN signal, the D2D UE may simultaneously receive a D2Dsignal and a WAN signal. Therefore, downlink carrier aggregation-capableUEs (DLCA-capable UEs) may simultaneously perform a D2D Rx on an uplinkspectrum and a WAN Rx on a downlink spectrum, when downlink carrieraggregation is not configured on a WAN (e.g., LTE WAN).

By taking into consideration the RF capability of a UE and thecharacteristics of a D2D signal, the frequency of a D2D Tx/Rx for D2Dcommunication may be expected to be higher than the frequency of a D2DTx/Rx for D2D discovery. Therefore, to minimize the deterioration in WANperformance, the method may assume that a UE that is capable ofperforming D2D communication configures an independent RF chain for aD2D communication signal and a WAN signal, and may define detailedoperations related thereto. In short, the UEs may be capable ofsimultaneously performing a D2D Rx and a WAN Rx in an FDD singlecarrier; thus it is easy to maintain a reliable radio link with respectto a WAN without affecting existing WAN signal reception.

Conversely, by taking into consideration the RF capability of a UE andthe characteristics of a D2D signal, the frequency of a D2D discoverysignal is expected to be lower than the frequency of a D2D communicationsignal. Therefore, the method may not assume that a UE that performs aD2D discovery always configures an independent RF chain for a D2Dcommunication signal and a WAN signal, and may define operations relatedthereto based on the same. For example, a UE that receives a D2Ddiscovery signal may perform a D2D Rx in the uplink and a WAN Rx in thedownlink in the FDD band based on a TDM scheme, using only a single Rxchain.

To this end, the multiplexing operation performed when a D2D Tx/Rxsignal and a WAN Tx/Rx signal collide will be described in associationwith a D2D discovery signal and a D2D communication, as follows.Hereinafter, the descriptions provided from the perspective of a D2Ddiscovery signal may be applied equally or similarly to a D2Dcommunication signal (or other signals).

First, FIGS. 13 to 16 are diagrams illustrating embodiments ofmultiplexing a D2D Rx associated with a D2D discovery signal and a WANRx.

FIG. 13 illustrates an embodiment (1-1) of a method of receiving a D2Ddiscovery signal through multiplexing of a D2D Rx and a WAN Rx accordingto the present disclosure.

Referring to FIG. 13, with respect to a subframe set as a resource or aresource pool 1311, 1312, 1313, and 1314 for receiving a D2D discoverysignal (e.g., type 1 or type 2B) within each D2D discovery period, a D2DUE monitors (or expects) a D2D discovery signal reception on an uplinkspectrum, and does not monitor (or expect) any signal on a downlinkspectrum 1321, 1322, 1323, and 1324.

In this instance, an Rx D2D UE may not be accurately aware of a D2Dresource through which a D2D discovery signal is to be received, andthus, the Rx D2D UE may not decode a channel (e.g., a PDCCH or ePDCCH)on a downlink spectrum with respect to a resource pool set for D2Ddiscovery signal reception, and may monitor D2D discovery signalreception.

FIG. 14 illustrates another embodiment (1-2) of a method of receiving aD2D discovery signal through multiplexing of a D2D Rx and a WAN Rxaccording to the present disclosure.

Referring to FIG. 14, with respect to a subframe set as a resource or aresource pool 1411, 1412, 1413, and 1414 for a D2D discovery signal(e.g., type 1 or type 2B) reception within each D2D discovery period, aD2D UE monitors (or expects) a WAN signal reception on a downlinkspectrum 1413, 1432, and 1433 when a subframe transferred by a servingeNB through a WAN Rx signal is at least one of the subframes 1) to 5) ofTable 1 provided below.

Conversely, when a subframe transferred by the serving eNB through a WANRx signal is different from the subframes 1) to 5) of Table 1, the D2DUE monitors (or expects) a D2D discovery signal reception on an uplinkspectrum and does not monitor (or expect) any signal on a downlinkspectrum 1421, 1422, and 1423.

TABLE 1 1) a subframe that requests or requires monitoring for receptionof a channel (e.g., a PDCCH or ePDCCH) with respect to at least one ofthese: System Information (SI), Paging, Random Access Response (RAR),Transmission Power Control (TPC), or MCCH change modification 2) asubframe through which a PBCH, a PSS, or an SSS is transmitted 3) asubframe in which a measurement gap is configured for measuring thechannel quality of an inter-carrier/inter-RAT 4) a subframe in which aUE wakes up for a downlink reception (DL Rx) when the UE performs adiscontinuous reception (DRX) operation (e.g., a subframe indicated bylong/short DRX cycle, a subframe before a timer expires, or the like) 5)an MBSFN subframe or a subframe for PMCH monitoring when a UE is capableof receiving an MBMS service (enabled)

Referring to Table 1, multiplexing of FIG. 10 may not be applied (thatis, multiplexing may be selectively applied) with respect to the DRXoperation of the UE of 4).

According to the multiplexing method of FIG. 14, a D2D UE may receivesignals for maintaining a link with a WAN and for effectively respondingto a predetermined service (e.g., MBMS). Monitoring only reception by aUE of the signals listed in Table 1 is allowed even in a D2D discoveryresource pool. Through the above, the method may perform a D2D discoveryand, at the same time, may minimize the effect on changing of importantsystem information of a WAN, maintaining an uplink access, powercontrol, an MBMS service, synchronization, channel measurement, and thelike.

As another example, with respect to a subframe that requires monitoringfor reception of at least one channel (e.g., a PDCCH or ePDCCH) that isscrambled to System Information (SI)/Paging (P)/Random Access(RA)/Transmission Power Control (TPC)/Multimedia Broadcast (M)/MulticastService (MBMS)-RNTI, and is detected from a common search space (CSS), aD2D UE may monitor a corresponding channel (e.g., a PDCCH or an ePDCCH)on a downlink spectrum even in a D2D discovery resource, and may decodethe same.

FIG. 15 illustrates another embodiment (1-3) of a method of receiving aD2D discovery signal through multiplexing of a D2D Rx and a WAN Rxaccording to the present disclosure.

Referring to FIG. 15, a D2D UE monitors D2D discovery signal receptionin only a few resources 1511 and 1521 in subframes 1510 and 1520, whichare set as a resource pool for receiving a D2D discovery signal (e.g.,type 1 or type 2B). The resources are referred to as configureddiscovery monitoring resources.

In this instance, a D2D UE always monitors (or expects) a D2D discoverysignal reception on an uplink spectrum in only a corresponding resource1511 or 1521, and monitors (or expects) reception of a WAN signal 1521or 1522 on a downlink spectrum with respect to the remaining D2Ddiscovery resources.

Particularly, the method of FIG. 11 may be more useful to the D2Ddiscovery type 2B since the first resource in a resource set configuredin a network (NW) may be a subframe.

The multiplexing method of FIG. 15 may solve a latency problemassociated with the reception of a D2D discovery signal and, at the sametime, may minimize the deterioration in performance and maintenanceassociated with a WAN link.

Also, the multiplexing method in FIG. 15 may configure a monitoringresource for a D2D discovery reception to be a subset smaller than orequaling a D2D discovery resource pool, and may use D2D discoveryresources for purposes other than the reception of a D2D discoverysignal. A D2D UE may not receive a D2D discovery signal transmitted froma predetermined D2D discovery Tx UE group according to the control of aneNB.

For example, a D2D discovery resource pool may be transferred to all D2Ddiscovery UEs in a cell through an SIB inside network (NW) coverage.However, in many cases, an Rx D2D UE may not need to monitor all D2Ddiscovery resources. Therefore, the Rx D2D UE may perform monitoringwith respect to a subset of resources configured according to an RRCsignal. Through the above, from the perspective of an Rx D2D UE, themethod may increase efficiency of the Rx D2D UE and may minimize theeffects on WAN downlink reception.

FIG. 16 illustrates another embodiment (1-4) of a method for receiving aD2D discovery signal through multiplexing of a D2D Rx and a WAN Rxaccording to the present disclosure.

Referring to FIG. 16, a D2D UE monitors (expects) a D2D discoveryreception on an uplink spectrum until the D2D UE receives a D2Ddiscovery signal in a first D2D discovery resource 1611 and 1621 fromamong subframes 1600 configured as a resource pool for a D2D discoveryreception (e.g., type 1 or type 2B), and successfully receives ordecodes an MAC PDU of the corresponding D2D discovery signal as shown inthe diagrams 1615 and 1625. In this instance, the first D2D discoveryresource may be a first resource for a D2D discovery transmissionresource set. Therefore, when the D2D UE accurately decodes and receivesthe D2D discovery signal in the first D2D discovery resource from amongthe subframes configured as a resource pool for a D2D discovery (type 1or type 2B) reception, the D2D UE monitors (expects) reception of a WANdownlink signal on a downlink spectrum in the remaining resources 1613and 1623 after excluding the first D2D discovery resource from the D2Ddiscovery resource set.

FIGS. 17 and 18 are diagrams illustrating examples of applyingmultiplexing of a D2D Rx and a WAN Rx to a plurality of discoveryresources according to the present disclosure.

Referring to FIG. 17, because a resource 1701 (e.g., a subframe) on thetime domain of a first resource for Tx/Rx in a single discovery periodof a cell is known (by specification with deterministic resources forretransmission of discovery), a D2D UE monitors (expects) D2D discoveryreception in the corresponding first resource, determines whether tomonitor the remaining resources (deterministic resources forretransmission) based on whether D2D discovery reception is successfullyperformed, and determines whether to receive a WAN downlink signal on adownlink spectrum.

Referring to FIG. 18, the embodiment of FIG. 17 may be extended to thecase in which multiple different resource periods are configured in acell.

Referring again to FIG. 16, when a D2D discovery reception issuccessfully performed in the first resource, a next resource mayinclude an RF retuning time 1617 and 1627 of at least several μs to ms.A single gap may be defined for the abovementioned time, which may begenerated through rate matching or puncturing.

A D2D UE receives a D2D discovery until a corresponding D2D discoveryMAC PDU is successfully received (or decoded) in the first D2D discoveryresource or in a subframe in which the remaining repeated transmissionsare expected to be performed. This process increases the probability ofsuccessfully receiving a D2D discovery MAC PDU in a single D2D discoveryperiod, and thus increases the probability of effectively utilizing aresource.

In this instance, a single D2D discovery Rx UE may increase theprobability of successful discovery reception during a given discoveryperiod and may thus decrease latency in a D2D discovery.

Second, embodiments of multiplexing a D2D Rx and a WAN Rx in associationwith a D2D communication signal will be described.

When a basic RF capability of a D2D UE is assumed to be a singletransceiver chain with respect to a D2D communication signal (e.g., SAin mode 1/2, or when a UE that is capable of simultaneously performing aWAN Rx in the downlink and a D2D RX in the uplink in association withD2D communication is assumed), additional multiplexing methods of thefollowing embodiments may be applied. Particularly, differentconsiderations associated with the SA may be applied to an SA resourcepool, when compared to the embodiments of the D2D discovery.

According to one embodiment (1-5), a D2D UE always monitors (or expects)reception of a communication signal on an uplink spectrum in thesubframes of a resource pool for reception of a D2D communication signal(e.g., SA in mode 1/2). Therefore, the D2D UE does not monitor (orexpect) reception of a communication signal on a downlink spectrum inthe subframes of the corresponding reception resource pool. Thisinstance may minimize latency of successful decoding of a D2Dcommunication signal.

According to another embodiment (1-6), when information that acorresponding serving eNB transfers through a WAN Rx on a downlinkspectrum, with respect to the subframes in a resource pool for receivinga D2D communication signal (e.g., SA in mode 1/2), is at least one ofthe subframes 1) to 4) of Table 2 provided below, a UE monitors (orexpects) reception on the downlink spectrum, and performs a relatedoperation. Otherwise, the UE monitors (or expects) reception of a D2Dcommunication signal (e.g., SA in mode 1/2) in the subframes in acommunication signal reception resource pool.

TABLE 2 1) a subframe that requests or requires monitoring for receivinga channel (e.g., a PDCCH or ePDCCH) associated with at least one ofSI/paging/RAR/TPC/MCCH change modifications 2) a subframe through whicha PBCH/PSS/SSS is transmitted 3) a subframe in which a measurement gapfor measuring the channel quality of an inter- carrier/inter-RAT 4) asubframe in which a UE wakes up for a downlink reception (DL Rx) whenthe UE performs a discontinuous reception (DRX) operation (e.g., asubframe indicated by long/ short DRX cycle, a subframe before anactivity timer expires, or the like)

Referring to FIG. 16, for reception between a downlink spectrum and anuplink spectrum (TDM with RF switching), a time 1617 and 1627 for RFretuning may be needed between two spectrums of a single transceiverchain. In this instance, a time gap may be proposed for providing a timefor RF retuning.

Case 2: Multiplexing D2D Rx and WAN Tx

It will be described that multiplexing is performed in order to transfera D2D Rx and a WAN Rx on an uplink spectrum.

Irrespective of the RF capability (e.g., single/double transceiverchain) of a UE, it is not allowed to simultaneously perform a D2D Rx anda WAN Tx (e.g., full duplex D2D Rx/WAN Tx) in a single uplinkspectrum/subframe (e.g., FDD/TDD). Therefore, the embodiments of FIGS.19 to 21 are proposed to avoid a collision between a D2D Rx and a WANTx. The embodiments may be applied to only a single D2D signal (e.g., aD2D communication signal [mode 1/2]), a D2D discovery signal (type 1/2),or a synchronization signal (D2DSS or PD2DSCH). The embodiments may alsobe applied to only some D2D signals, or may be applied to only apredetermined mode or type.

FIG. 19 is a diagram illustrating an example (2-1) of multiplexing a D2DRx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

Referring to FIG. 19, when transmission of a WAN uplink signal isscheduled or configured in advance in a resource pool for reception of aD2D signal (e.g., a D2D discovery signal [type 1 or type 2] or a D2Dcommunication signal [SA, mode 1/2]) or resources for reception 1901,1902, 1903, and 1904 in a resource pool, a WAN uplink signal ispreferentially transmitted, and monitoring (or decoding) of reception ofa D2D signal is not performed. For example, a WAN uplink signal that istransmitted in preference to monitoring of a D2D signal may include aHARQ-ACK 1911, a PRACH 1912, an aperiodic SRS/CSI, an SR 1913, or thelike. Through the above, deterioration in WAN performance may beminimized.

More particularly, an embodiment will be described in which a WAN uplinksignal that is scheduled in advance is preferentially transmitted to aD2D UE, and monitoring (or decoding) of a D2D reception signal is notperformed.

An example (2-1-1) corresponds to the remaining cases, excluding thecase in which an SRS or a CSI (e.g., a periodic CSI and/or an aperiodicCSI) from among WAN uplink signals is transmitted in a resource pool forreceiving a D2D signal or is transmitted in the resources in a resourcepool (e.g., a D2D discovery resource pool, resources for reception in aresource pool, a resource pool for receiving a D2D communication signal[SA, Mode 1/2], or resources for reception in a resource pool). That is,only when an SRS or a CSI from among WAN uplink signals is transmittedin a D2D reception resource pool/configured resources, a D2D UE monitors(or decodes) reception of a D2D signal, and may drop the SRS or the CSI,which is the corresponding WAN uplink transmission signal.

According to another example (2-1-2), when transmission of an aperiodicSRS or aperiodic CSI is performed at the same time as monitoring ofreception of a D2D signal in the same uplink subframe, the aperiodic SRSor the aperiodic CSI is transmitted and monitoring (or decoding) of thereception of the D2D signal may be skipped. In this instance, whentransmission of a periodic SRS or a periodic CSI 1914 is performed atthe same time as monitoring of reception of a D2D signal in the sameuplink subframe, the monitoring (or decoding) of the reception of theD2D signal is performed and the transmission of the periodic SRS or theperiodic CSI may be dropped.

According to another example (2-1-3), when the CSI reporting typecorresponds to at least one of “3, 5, 6, and 2a”, the corresponding CSIreport is performed and monitoring (or decoding) of the reception of aD2D signal may be dropped. That is, in a D2D resource, a WAN uplinktransmission associated with CSI reporting of type 3, 5, 6, or 2a may beprioritized over the reception of a D2D signal. However, for other CSIreporting types, reception of a D2D signal is preferentially performed.

FIG. 20 is a diagram illustrating an example (2-2) of multiplexing a D2DRx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

Referring to FIG. 20, when a WAN uplink signal associated with a PUCCHor PUSCH (or PUSCH retransmission) and including at least one piece ofcontrol information is scheduled (or configured) in a resource pool forreceiving a D2D discovery (type 1/2), a D2D communication (SA, Mode 1/2)signal, or resources for reception in a resource pool, a WAN uplinksignal is preferentially transmitted. In this instance the process skipsmonitoring (or decoding) reception of a D2D signal.

The PUCCH or PUSCH including the control information may be, forexample, a PUCCH or a PUSCH including at least one of: a PRACH, aHARQ-ACK 2001, an SR 2002 (or BSR), a message responsive to an RARmessage (e.g., message 3), or Data (PUSCH) retransmissions 2003. In thisinstance, reception of a WAN uplink signal associated with a PUCCH or aPUSCH for purposes other than corresponding control information may beskipped, and D2D signal reception may be monitored (or decoded) in thecorresponding D2D resource pool or in configured resources.

Through the above, a WAN uplink transmission that transfers the maincontrol information may be secured in preference to a D2D signal.

FIG. 21 is a diagram illustrating another example (2-3) of multiplexinga D2D Rx and a WAN Tx on an uplink spectrum according to the presentdisclosure.

Referring to FIG. 21, one of the DL-reference UL/DL configurations(e.g., Table 3) defined as a downlink HARQ timing for an FDD secondaryserving cell in “TDD-FDD TDD (PCell)-FDD(SCell) CA in self-scheduling”is configured through higher layer scheduling in a resource pool forreceiving a D2D discovery (e.g., type 1/2), D2D communication (e.g., SA,mode 1/2), or resources for reception in a resource pool. Through theabove, the effect of a HARQ-ACK transmission associated with a downlinkPDSCH transmission among WAN uplink transmission signals may beminimized. An eNB appropriately schedules (configures) a transmissionresource and may enable data (e.g., PUSCH) and a signal (e.g., a CSI,SRS, SR, PRACH, or the like) to be transmitted in resources excluding aD2D resource.

In FIG. 21, a DL-reference HARQ configuration indicates that a HARQ-ACK2102, 2112, 2122, and 2132 is transferred after a D2D reception resourcepool 2101, 2111, 2121, and 2131. WAN data 2103 and 2113 and an SRS/CSItransmission frame 2143 are transmitted, respectively, after theHARQ-ACK 2102, 2112, 2122, and 2132.

Table 3 illustrates the downlink association set index (K:{k₀, k₁, . . ., k_(M-1)}) associated with an FDD-TDD and serving cell frame structuretype 1.

TABLE 3 DL-reference Subframe n UL/DLConfiguration 0 1 2 3 4 5 6 7 8 9 0— — 6, 5 5, 4 4 — — 6, 5 5, 4 4 1 — — 7, 6 6, 5, 4 — — — 7, 6 6, 5, 4 —2 — — 8, 7, 6, 5, 4 — — — — 8, 7, 6, 5, 4 — — 3 — — 11, 10, 9, 8, 7, 66, 5 5, 4 — — — — — 4 — — 12, 11, 10, 9, 8, 7 7, 6, 5, 4 — — — — — — 5 —— 13, 12, 11, 10, 9, 8, 7, 6, 5, 4 — — — — — — — 6 — — 8, 7 7, 6 6, 5 —— 7 7, 6, 5 —

Referring to Table 3, n denotes a subframe number. The downlink subframeset associated with a subframe having the corresponding number isdetermined by K={k0, k1, . . . , kM-1}. n-k indicates a subframe indexof the subframe located k subframes before an n^(th) subframe, whichindicates the downlink subframe associated with a current subframe. Anassociated downlink subframe indicates a subframe that carries a PDSCHused for determining an ACK/NACK signal, or that carries a PDCCHindicating a DL SPS release. M denotes the number of elements in the setK defined in Table 3, and indicates the number of downlink subframesassociated with the n^(th) subframe.

For example, when a DL-reference UL/DL configuration corresponding to asingle serving cell is “1”, M=2 is associated with a downlinkassociation set K for subframe #2, k0=7, and k1=6. Therefore, downlinksubframes associated with the subframe #2 of the corresponding servingcell are the subframe #5 (2-k0) and subframe #6 (2-k1) of a previousradio frame. Also, for example, when the DL reference UL/DLconfiguration is “2”, the subframe numbers associated with subframe #2may be 8, 7, 6, 5, and 4, and the subframe numbers associated withsubframe #7 may also be 8, 7, 6, 5, and 4.

According to an example (2-3-1), a higher layer signal may be configuredin a DL-reference UL-DL configuration sub-set including some of theseven DL-reference UL/DL configurations of Table 3, as opposed to beingconfigured to support all of the seven DL-reference UL/DLconfigurations. In this instance, the DL-reference UL-DL configurationsub-set may be configured to always include DL-reference UL-DLconfiguration #5.

For example, an eNB may select one of the DL reference UL-DLconfigurations #2, #4, and #5 from a higher layer signal configured in aDL-reference UL-DL configuration sub-set including the DL referenceUL-DL configurations #2, #4, or #5. The selected DL reference willresult in a relatively low-frequency HARQ-ACK transmission, and may setthe selected DL-reference UL-DL configuration for D2D UEs.

According to another example (2-3-2), when it is inevitable that alimited WAN signal transmission and a D2D signal reception are performed(that is, when they collide) in the same resource even though the methodof FIG. 21 is used, an eNB and a UE may always perform a WAN signaltransmission first. For example, an uplink resource environment islimited due to “TDD, a limited system BW, or a WAN uplink SPStransmission” or the like, and thus, when a WAN signal transmission anda D2D signal reception collide, an eNB and a UE may always perform a WANsignal transmission first.

The method in FIG. 21 relies on the fact that a HARQ-ACK transmissionoperated in an FDD band may be performed in all uplink subframes (e.g.,a subframe n) based on scheduling on a downlink subframe (e.g., subframen-4). A HARQ-ACK transmission in a D2D resource may be avoided throughscheduling constraints, such as uplink data scheduling, but this maycause deterioration in WAN downlink performance, which is a drawback.

Therefore, the method of FIG. 21 may avoid the collision between aHARQ-ACK transmission and a D2D resource, and at the same time may applya downlink HARQ timing (DL HARQ timing) introduced in a TDD-FDD CA,thereby becoming capable of performing data scheduling in all FDDdownlink subframes.

According to another example (2-4), when a collision with a WAN uplinktransmission occurs in a resource pool for receiving a D2D discovery(type 1/2) signal or resources for reception in a resource pool, a D2DUE always receives a D2D discovery signal (or receives only a type 1 D2Ddiscovery signal). When a collision with a WAN uplink transmissionoccurs in a resource pool for receiving a D2D communication (SA) signalor resources for reception in a resource pool, a

D2D UE always transmits a WAN uplink signal.

Case 3: Multiplexing D2D Tx and WAN Tx

A D2D Tx and a WAN Tx may not be simultaneously transmitted on a singlecarrier (e.g., on an uplink spectrum of an FDD carrier). That is, FDM isnot allowed and only TDM is allowed.

Similar to Case 2, a D2D UE may perform only one of a D2D signaltransmission or a WAN signal transmission (but may not be capable ofperforming the remaining one).

Unlike Case 2, a D2D discovery or communication transmission resourceneeds to be considered.

Particularly, D2D discovery type 1 defines an operation when a collisionwith a WAN transmission signal occurs in a D2D discovery resource setutilized for transmitting (or retransmitting) a D2D discovery signal(that is, when a D2D discovery signal transmission and a WAN signaltransmission are simultaneously performed). A resource for transmissionof D2D discovery signal type 1 is randomly selected by a Tx UE, and aneNB may not have information about whether the corresponding resource isto be used by the Tx D2D UE.

Conversely, D2D discovery type 2B corresponds to the case in which acollision with a WAN signal transmission occurs in a D2D discoveryresource indicated by an eNB. In D2D discovery type 2B, unlike in D2Ddiscovery type 1, an eNB controls the utilization of resources; thus, acollision between a D2D discovery signal transmission and a WANtransmission signal may be avoided according to scheduling orconfiguration by the eNB.

Hereinafter, a method of multiplexing a D2D discovery signaltransmission and a WAN signal transmission will be described.

First, D2D discovery type 1 considers a D2D resource set in a D2Dresource period. D2D communication (e.g., SA in mode 2) considers aresource pool for a D2D signal transmission.

Case 3 also assumes that the considerations of WAN signal transmissionare the same as described above, and a method obtained by applying thefollowing description to the methods proposed in Case 2 may be utilizedas a method for Case 3.

First, an embodiment will be described in which a WAN uplink signal thatis scheduled in advance is preferentially transmitted to a D2D UE, andtransmission (or monitoring of transmission) of a D2D signal is notperformed. Through the above, deterioration in WAN performance may beminimized.

As an embodiment (3-1), when a WAN uplink transmission is scheduled orconfigured in advance in a D2D discovery (e.g., type 1/2) resource setor a resource pool (transmission resource pool) for transmission of aD2D communication signal (SA in mode 2), a WAN uplink signal ispreferentially transmitted and a D2D signal (e.g., a D2D discoverysignal or a D2D communication signal) is not transmitted.

As an example (3-1-1), the case in which a WAN uplink signal ispreferentially transmitted corresponds to the remaining cases, excludingthe case in which an SRS or a CSI (e.g., periodic CSI and/or aperiodicCSI) is transmitted in a resource set for transmission of a D2Ddiscovery signal (type 1/2) or in a resource pool for transmission of aD2D communication signal (SA, mode 1/2). That is, only when an SRS or aCSI from among WAN uplink signals is transmitted in a D2D transmissionresource set or in a resource pool for transmission of a D2Dcommunication signal, a D2D UE preferentially transmits a D2D signal,and may drop the SRS or the CSI, which is the corresponding WAN uplinktransmission signal.

As another example (3-1-2), when transmission of an aperiodic SRS oraperiodic CSI is performed at the same time as transmission (ormonitoring of transmission) of a D2D signal in the same uplink subframe,the aperiodic SRS or the aperiodic CSI is transmitted and thetransmission (or monitoring of the transmission) of the D2D signal maybe skipped. In this instance, when transmission of a periodic SRS or aperiodic CSI is performed at the same time as transmission of a D2Dsignal in the same uplink subframe, the transmission (or monitoring ofthe transmission) of the D2D signal is performed and the transmission ofthe periodic SRS or the periodic CSI may be dropped.

As another example (3-1-3), when a reporting type of a CSI reporting isat least one of “3, 5, 6, and 2a”, the corresponding CSI reporting maybe performed and transmission of a D2D signal may be dropped. That is,in a D2D resource, a WAN uplink transmission associated with a CSIreporting of “type 3, 5, 6, or 2a” is performed in preference totransmission of a D2D signal.

Second, according to another embodiment (3-2), a WAN uplink signalassociated with a PUCCH or a PUSCH (or a PUSCH retransmission) andincluding at least one piece of control information is preferentiallytransmitted in a D2D discovery (e.g., type 1/2) resource set or in aresource pool for transmission of a D2D communication (SA, mode 1/2)signal, and a D2D signal transmission is skipped. The PUCCH or PUSCHincluding the at least one piece of control information may be, forexample, a PUCCH or a PUSCH including at least one of: a PRACH, aHARQ-ACK, an SR (or BSR), a message responsive to an RAR message (e.g.,message 3), and Data (PUSCH) retransmissions.

In this instance, transmission of a WAN uplink signal associated with aPUCCH or a PUSCH including information other than the correspondingcontrol information may be skipped, and a D2D signal is transmitted inthe corresponding D2D discovery resource set or in the resource pool fortransmission of a D2D communication signal.

Through the above, a WAN uplink transmission that transfers main controlinformation may be secured in preference to a D2D signal.

Third, according to another embodiment (3-3), one of the DL-referenceUL/DL configurations (e.g., Table 3), defined as a downlink HARQ timing(DL HARQ timing) for an FDD secondary serving cell in“TDD(PCell)-FDD(SCell) CA in self-scheduling,” is configured through ahigher layer scheduling in a D2D discovery (e.g., type 1/2) resource setor in a resource pool for transmission of a D2D communication (e.g., SA,mode 1/2) signal. Through the above, the effect of a HARQ-ACKtransmission associated with a downlink PDSCH transmission among WANuplink transmission signals may be minimized. An eNB appropriatelyschedules (or configures) a transmission resource and may enable data(e.g., a PUSCH) and a signal (e.g., a CSI, SRS, SR, PRACH, or the like),which need to be transferred in another uplink, to be transferred inresources excluding a D2D resource.

According to an embodiment, a higher layer signal may be configured in aDL-reference UL-DL configuration sub-set including some of the sevenDL-reference UL/DL configurations of Table 3, as opposed to beingconfigured to support all of the seven DL-reference UL/DLconfigurations. In this instance, the DL-reference UL-DL configurationsub-set may be configured to always include DL-reference UL-DLconfiguration #5.

For example, an eNB may select one of DL reference UL-DL configurations#2, #4, and #5 from a higher layer signal, which is configured in aDL-reference UL-DL configuration sub-set including DL reference UL-DLconfigurations #2, #4, or #5 having the relatively low frequency of aHARQ-ACK transmission, and may set the selected DL-reference UL-DLconfiguration for D2D UEs.

As another example, when it is inevitable that a limited WAN signaltransmission and a D2D signal transmission are performed (that is,collide) in the same resource even though the above described embodimentis used, an eNB and a UE may always perform a WAN signal transmissionfirst. For example, when an uplink resource environment is limited dueto “TDD, a limited system BW, or a WAN uplink SPS transmission” or thelike and thus a WAN signal transmission and a D2D signal transmissioncollide, an eNB and a UE may always perform a WAN signal transmissionfirst.

The above described embodiment takes as a given that a HARQ-ACKtransmission operated in an FDD band may be performed in all uplinksubframes (e.g., a subframe n) based on scheduling in a downlinksubframe (e.g., subframe n-4). A HARQ-ACK transmission in a D2D resourcemay be avoided through scheduling constraints, such as an uplink datascheduling, but this may cause deterioration in WAN downlinkperformance.

Therefore, the above described embodiment may avoid the collisionbetween a HARQ-ACK transmission and a D2D resource and, at the sametime, may apply the downlink HARQ timing (DL HARQ timing) introduced inTDD-FDD CA, thereby becoming capable of performing data scheduling inall FDD downlink subframes.

Fourth, according to another embodiment (3-4), when a collision with aWAN uplink transmission occurs in the resources of a D2D discovery (type1/2) resource set, a D2D discovery signal is always transmitted (or onlya D2D discovery signal of type 1 is transmitted). When a collision witha WAN uplink signal occurs in a resource pool for transmission of a D2Dcommunication (SA) signal, a WAN uplink signal is always transmitted.

The embodiments of Case 3 may be applied to only a single D2D signal(e.g., a D2D communication signal (mode 1/2)), a D2D discovery signal(type 1/2), or a synchronization signal (D2DSS or PD2DSCH).Alternatively, the embodiments of Case 3 may be applied to only some D2Dsignals, or may be applied to only a predetermined mode or type.

Case 4: Multiplexing a D2D Tx and a WAN Rx

On a single carrier (e.g., on an uplink spectrum of an FDD carrier), aD2D Tx in the uplink and a WAN Rx in the downlink may be performed inparallel as before, and thus, multiplexing may not be needed.

Although Case 1 to Case 4 have been described based on an FDD carrier,the descriptions may also be applied to TDD. In this instance, TDDconsiders an uplink subframe, instead of an uplink spectrum on an FDDcarrier. Particularly, the embodiment may be utilized for multiplexing aD2D transmission and a WAN transmission.

FIG. 22 is an example of a flowchart illustrating operations of a UEaccording to the present disclosure.

Referring to FIG. 22, a UE determines whether a D2Dtransmission/reception and a WAN transmission/reception collide inoperation S2200. That is, the UE determines whether a collision occursbecause a D2D signal transmission/reception and a WAN signaltransmission/reception are configured or scheduled to be performed inparallel in the same spectrum/subframe.

When a collision occurs, the UE determines priority of the D2Dtransmission/reception and the WAN transmission/reception in operationS2210. The UE determines a signal to be transmitted/received accordingto Case 1 through Case 4 described in FIGS. 13 to 21, and performsmultiplexing.

The UE transmits or receives the corresponding signal to a UE or an eNBaccording to the determination in operation S2220.

FIG. 23 is an example of an apparatus block diagram of a wirelesscommunication system according to the present disclosure.

Referring to FIG. 23, a UE 2300 includes a UE transmitting unit 2305, aUE receiving unit 2310, and a UE processor 2320. The UE may furtherinclude a memory (not illustrated). The memory is connected with the UEprocessor 2320, and stores various pieces of information used foroperating the UE processor 2320. In the above described embodiments, theoperations of the UE 2300 may be implemented under the control of theprocessor 2320. The UE processor 2320 may further include a collisiondetermining unit 2325 and a multiplexing unit 2330.

The UE transmitting unit 2305 executes transmission of a D2D signal ortransmission of a WAN signal.

The UE receiving unit 2310 executes reception of a D2D signal orreception of a WAN signal.

The collision determining unit 2325 determines whether a collisionoccurs because a D2D signal transmission/reception and a WAN signaltransmission/reception are set or scheduled to simultaneously performedin the same spectrum/subframe.

The multiplexing unit 2330 may determine a signal to betransmitted/received in the corresponding spectrum/subframe according toCase 1 through Case 4 described in FIGS. 13 to 21. The multiplexing unit2330 may be also referred to as a scheduling unit because it performsthe function of scheduling a signal to be transmitted/received.

More particularly, a multiplexing method according to Case 1 throughCase 4 will be described as follows.

According to Case 1 (D2D Rx and WAN Rx), the multiplexing unit 2330 mayperform multiplexing to enable a D2D UE to monitor reception of a D2Ddiscovery signal on an uplink spectrum. The multiplexing unit 2330 mayalso perform multiplexing to enable a D2D UE to not monitor any signalon a downlink spectrum or in a spectrum/subframe configured as resourcesor a resource pool for reception of a D2D discovery signal within eachD2D discovery period.

As another example, the multiplexing unit 2330 may perform multiplexingto enable a D2D UE to monitor a WAN signal reception on a downlinkspectrum and to perform a related operation when a subframe that an eNBtransfers through a WAN Rx signal is at least one of the subframes ofTable 1 (signals for maintaining a link with a WAN and for effectivelyresponding to a predetermined service), with respect to a subframeconfigured as a resource or a resource pool for reception of a D2Ddiscovery signal within each D2D discovery period.

Conversely, when the subframe that the serving eNB transfers through theWAN Rx signal is different from the subframes of Table 1, themultiplexing unit 2330 may perform multiplexing to enable the D2D UE tomonitor reception of a D2D discovery signal on an uplink spectrum andnot to monitor any signal on a downlink spectrum.

As another example, the multiplexing unit 2330 may perform multiplexingto a D2D UE to monitor reception of a D2D discovery signal only in someresources of subframes configured as a resource pool for reception of aD2D discovery signal. In this instance, the multiplexing unit 2330 mayperform multiplexing to the D2D UE to always monitor reception of a D2Ddiscovery signal on an uplink spectrum in only the correspondingresources, and to monitor reception of a WAN signal on a downlinkspectrum in the remaining D2D discovery resources.

As another example, the multiplexing unit 2330 may perform multiplexingin a D2D UE to monitor a D2D discovery reception on an uplink spectrumuntil a D2D discovery signal is received in the first D2D discoveryresource from among the subframes configured as a resource pool for aD2D discovery reception, and until an MAC PDU of the corresponding D2Ddiscovery signal is successfully received or decoded.

As another example, the multiplexing unit 2330 may perform multiplexingin a D2D UE to always monitor reception of a communication signal on anuplink spectrum in the subframes of a resource pool for reception of aD2D communication signal, and to not monitor reception of acommunication signal on a downlink spectrum in the subframes of thecorresponding reception resource pool.

As another example, the multiplexing unit 2330 may perform multiplexingin a D2D UE to monitor reception on a downlink spectrum and also toperform a related operation when information transferred by acorresponding serving eNB through a WAN Rx on a downlink spectrum in thesubframes of a resource pool for reception of a D2D communication signalis at least one of the subframes of Table 2. Otherwise, the D2D UEmonitors reception of a D2D communication signal.

According to Case 2 (D2D Rx and WAN Tx), the multiplexing unit 2330performs multiplexing in a D2D UE to preferentially transmit a WANuplink signal and to not perform monitoring (or decoding) of D2D signalreception when transmission of a WAN uplink signal is scheduled orconfigured in advance in a resource pool for reception of a D2D signalor in the resources for reception in a resource pool. For example, onlywhen transmission of an SRS or a CSI from among WAN uplink signalsoccurs in a D2D reception resource pool (or in configured resources),the multiplexing unit 2330 may perform multiplexing in a D2D UE tomonitor reception of a D2D signal and to drop the SRS or the CSI, whichis the corresponding WAN uplink transmission signal. As another example,when transmission of an aperiodic SRS or an aperiodic CSI occurs at thesame time as monitoring reception of a D2D signal in the same uplinksubframe, the multiplexing unit 2330 may perform multiplexing in a D2DUE to transmit the aperiodic SRS or the aperiodic CSI and to skipmonitoring of D2D signal reception. As another example, when thereporting type of a CSI report is at least one of “3, 5, 6, and 2a”, themultiplexing unit 2330 may perform multiplexing in a D2D UE to performthe corresponding CSI reporting and to drop reception of a D2D signal.

As another example, when a WAN uplink signal associated with a PUCCH ora PUSCH and including at least one piece of control information isscheduled in a resource pool for a D2D discovery signal or a D2Dcommunication signal reception or resources for reception in a resourcepool, the multiplexing unit 2330 may perform multiplexing in a D2D UE topreferentially transmit a WAN uplink signal, and to skip monitoring of aD2D signal reception.

As another example, the multiplexing unit 2330 may perform multiplexingin a D2D UE to configure one of DL-reference UL/DL configurationsdefined as a downlink HARQ timing for an FDD secondary serving cell in“TDD-FDD TDD(PCell)-FDD(SCell) CA in self-scheduling” in a resource poolfor a D2D discovery or D2D communication reception or resources forreception in a resource pool, through a higher layer signal.

As another example, the multiplexing unit 2330 may perform multiplexingto enable a D2D UE to always receive a D2D discovery signal when acollision with a WAN uplink transmission occurs in a resource pool forreception of a D2D discovery signal or in the resources for reception ina resource pool, and may perform multiplexing to enable the D2D UE toalways transmit a WAN uplink signal when a collision with a WAN uplinktransmission occurs in a resource pool for reception of a D2Dcommunication signal or the resources for reception in a resource pool.

According to Case 3 (a D2D Tx and a WAN Tx), the multiplexing unit 2330may perform multiplexing by applying the embodiment of Case 2 to a D2DTx, as opposed to a D2D Rx.

In the case of D2D discovery type 1, the multiplexing unit 2330 mayperform multiplexing when a collision with a WAN transmission signaloccurs in a D2D discovery resource set to be utilized for transmissionof a D2D discovery signal. In this instance, a resource for transmissionof D2D discovery signal type 1 is randomly selected by a Tx UE, and aneNB 2350 may not have information about whether the correspondingresource is to be used by the Tx D2D UE.

Conversely, in the case of D2D discovery type 2B, the multiplexing unit2330 may perform multiplexing when a collision with a WAN signaltransmission occurs in a D2D discovery resource indicated by the eNB2350. In D2D discovery type 2B, the eNB 2350 controls the utilization ofresources more closely when compared to D2D discovery type 1, and thus,a collision between a D2D discovery signal transmission and a WANtransmission signal may be avoided according to scheduling orconfiguration by the eNB.

The eNB 2350 includes an eNB receiving unit 2355, an eNB transmittingunit 2360, and an eNB processor 2370. The eNB 2350 may further include amemory (not illustrated). The memory is connected with the eNB processor2370, and stores various pieces of information used for operating theeNB processor 2370. In the above described embodiments, the operationsof the eNB 2350 may be implemented under the control of the eNBprocessor 2370. The eNB processor 2370 may include an RRC connectiondetermining unit 2375, a D2D resource allocation unit 2380, and a D2Dmode setting unit 2385.

The eNB transmitting unit 2360 may transmit D2D configurationinformation to the UE 2300.

The RRC connection determining unit 2375 may determine whether the UE2300 is in an idle mode or an RRC-connected mode.

The D2D mode setting unit 2385 may set a D2D mode of the UE 2300.

The D2D resource allocation unit 2380 may generate informationassociated with a resource pool for D2D communication, based on whetherthe UE 2300 is in an idle mode or an RRC-connected mode. Also, the D2Dresource allocation unit 2380 may generate D2D configurationinformation. The D2D configuration information may include configurationinformation associated with

D2D discovery type 1/type 2, information associated with a correspondingTx/Rx resource pool, and the like. The D2D configuration information mayinclude information associated with a D2D resource pool for D2D mode2/mode 1. A resource for monitoring a D2D discovery reception may beconfigured in the form of a subset, which is smaller than or equal tothe D2D discovery resource pool. The D2D configuration information mayinclude information associated with a D2D monitoring period (i.e.,monitoring resource information). The monitoring resource informationmay include only information associated with a period where D2D signalsof D2D UEs that access a network of a single operator are monitored, ormay also include information associated with a period where D2D signalsof D2D UEs that access the network of another operator are monitored.

What is claimed is:
 1. A User Equipment (UE) of performing a randomaccess procedure during a device-to-device (D2D) discovery period, theUE comprising: a transceiver; and a processor operationally coupled tothe transceiver and configured to receive through Radio Resource Control(RRC) signaling, information of a resource pool for a D2D communication,wherein the information of the resource pool comprises information of adiscovery subframe in which a D2D discovery signal is to becommunicated; the processor is further configured to determine that inthe discovery subframe, the D2D discovery signal is prioritized over acommunication with an evolved NodeB (eNB) unless the communication withthe eNB is associated with a random access (RA) procedure; the processoris further configured to transmit a RA preamble through a PhysicalRandom Access Channel (PRACH); the processor is further configured todetermine whether the discovery subframe corresponds to a RA subframe inwhich a RA response for the UE is to be monitored; and determine thatthe discovery subframe corresponds to the RA subframe, monitoring the RAresponse during the discovery subframe.
 2. The UE of claim 1, whereinthe processor is further configured to determine that the discoverysubframe corresponds to the RA subframe, ceasing to monitor reception ofthe D2D discovery signal during the discovery subframe.
 3. The UE ofclaim 1, wherein the processor is further configured to determine thatthe discovery subframe does not correspond to the RA subframe,monitoring, by the UE, reception of the D2D discovery signal during thediscovery subframe, wherein the discovery subframe corresponds to adiscovery reception subframe in which the UE monitors the D2D discoverysignal transmitted from a different UE.
 4. The UE of claim 1, whereinthe processor is further configured to refrain from monitoring adownlink signal transmitted from the eNB while monitoring the receptionof the D2D discovery signal during the discovery subframe.
 5. The UE ofclaim 1, wherein the processor is further configured to determine thatthe discovery subframe does not correspond to the RA subframe,transmitting, by the UE, the D2D discovery signal during the discoverysubframe, wherein the discovery subframe corresponds to a discoverytransmission subframe in which the UE transmits the D2D discovery signalto discover a different UE.
 6. The UE of claim 1, wherein the processoris further configured to establish, an RRC connection with the eNB or adifferent eNB; and receive the RA response for the UE based on themonitoring during the discovery subframe.
 7. A User Equipment (UE) ofperforming a random access procedure during a device-to-device (D2D)discovery period, the UE comprising: a transceiver; and a processoroperationally coupled to the transceiver and configured to determine adiscovery period comprising one or more of a discovery transmissionsubframe or a discovery reception subframe, wherein the discoverytransmission subframe is configured for the UE to transmit a D2Ddiscovery signal to discover a different UE, and the discovery receptionsubframe is configured for the UE to monitor reception of a D2Ddiscovery signal transmitted from a different UE; the processor isfurther configured to determine that in the discovery period, a D2Ddiscovery communication between UEs is prioritized over a Wide AreaNetwork (WAN) communication with an evolved NodeB (eNB) unless the WANcommunication with the eNB is associated with a random access (RA)procedure; the processor is further configured to transmit a RA preamblethrough a Physical Random Access Channel (PRACH); the processor isfurther configured to determine a RA response monitoring period in whicha RA response for the UE is to be monitored; and determine that at leastpart of the RA response monitoring period overlaps the discovery period,and monitor the RA response during the overlapped discovery period. 8.The UE of claim 7, wherein the processor is further configured todetermine that at least part of the RA response monitoring periodoverlaps the discovery period, and cease to monitor the reception of aD2D discovery signal during the overlapped discovery period.
 9. The UEof claim 7, wherein the processor is further configured to monitorreception of a D2D discovery signal during the discovery receptionsubframe not overlapping the RA response monitoring period.
 10. The UEof claim 7, wherein the processor is further configured to refrain frommonitoring a downlink signal transmitted from the eNB while monitoringthe reception of a D2D discovery signal during the discovery receptionsubframe not overlapping the RA response monitoring period.
 11. The UEof claim 7, wherein the processor is further configured to transmit aD2D discovery signal during the discovery transmission subframe notoverlapping the RA response monitoring period.
 12. The UE of claim 7,wherein the processor is further configured to establish an RRCconnection with the eNB or a different eNB; and receive the RA responsebased on the monitoring during the overlapped discovery period.
 13. AUser Equipment (UE) of performing a random access procedure during adevice-to-device (D2D) discovery period, the UE comprising: atransceiver; and a processor operationally coupled to the transceiverand configured to receive and through Radio Resource Control (RRC)signaling, information of a resource pool for a D2D communication,wherein the information of the resource pool comprises information of adiscovery subframe in which a D2D discovery signal is to becommunicated; the processor is further configured to determine that inthe discovery subframe, the D2D discovery signal is prioritized over acommunication with an evolved NodeB (eNB) unless the communication withthe eNB is associated with a random access (RA) procedure; the processoris further configured to transmit a RA preamble through a PhysicalRandom Access Channel (PRACH); the processor is further configured todetermine a RA response received during a RA monitoring period in whichthe RA response for the UE is to be monitored; the processor is furtherconfigured to determine whether the discovery subframe corresponds to aRA subframe in which a message responsive to the RA response for the UEis to be processed; and determine that the discovery subframecorresponds to the RA subframe, processing the message responsive to theRA response during the discovery subframe.
 14. The UE of claim 13,wherein the processor is further configured to determine that thediscovery subframe corresponds to the RA subframe, and transmit, by theUE and to the eNB, the message responsive to the RA response during thediscovery subframe.
 15. The UE of claim 13, wherein the processor isfurther configured to determine that the discovery subframe correspondsto the RA subframe, ceasing to monitor reception of the D2D discoverysignal during the discovery subframe.
 16. The UE of claim 13, whereinthe processor is further configured to determine that the discoverysubframe does not correspond to the RA subframe, and monitor receptionof the D2D discovery signal during the discovery subframe, wherein thediscovery subframe corresponds to a discovery reception subframe inwhich the UE monitors the D2D discovery signal transmitted from adifferent UE.
 17. The UE of claim 13, wherein the processor is furtherconfigured to refrain from monitoring a downlink signal transmitted fromthe eNB while monitoring the reception of the D2D discovery signalduring the discovery subframe.
 18. The UE of claim 13, wherein theprocessor is further configured to determine that the discovery subframedoes not correspond to the RA subframe, transmitting, by the UE, the D2Ddiscovery signal during the discovery subframe, wherein the discoverysubframe corresponds to a discovery transmission subframe in which theUE transmits the D2D discovery signal to discover a different UE.